Syringes are commonly and largely used in the field of medical treatment. If the syringes are used repeatedly, it is likely to cause the diseases to spread among the different patients and result in cross infection which will endanger the health of the public people. In order to seek illegal gains, some persons collect the used and discard disposable syringes and put these syringes into the medical treatment market again. As a result, it will be a heavy threaten of spreading and proliferating many diseases. On the other hand, healthcare workers and the waste collecting persons may suffer from needlesticks after the completion of injection because of the expose of the needle heads so as to cause disease infections or spread.
In order to prevent repeatedly using the syringes and to make the syringes self-destruct immediately once they have been used so that the syringes can actually be used only one time and accidental needlesticks caused by the used syringes can be prevented from occurring, a solution concerning a needle-retractable disposable syringe has been proposed. Also, an improvement on the barrel type plunger used for this kind of syringe has been made so that the self-destruction of the syringes and the controllability of the needle retraction can be obtained.
As an example, Chinese utility model patent ZL200520015704.2 discloses a novel barrel type plunger used for a needle-retractable safety syringe and a safety syringe using with the same. As described in this Chinese patent, the bearing piece is controlled by the fitting of the outer barrel and the inner barrel of the barrel type plunger, and the bearing piece is used to control the retraction of the pushing post and the released needle carrier. In this way, the self-destruction of the syringes after the completion of injection and the controllability of the needle retraction can be realized. Moreover, it can prevent the syringes from being used repeatedly, and can eliminate a risk of accidental needlesticks caused by the exposed syringes needle after the completion of injection.
Although the solution as disclosed in the above-mentioned Chinese utility model patent can realize the controllability of the syringe needle retraction after the injection, this solution has the following defects: (1) the structure of the barrel type plunger is relatively complex so that it is rather difficult for the barrel type plunger to be produced and the assembling procedure is relatively complex, thereby the production cost is relatively high; (2) since the structure of the barrel type plunger is relatively complex, it is hardly to be suitable for a syringe having minor milliliter volume, such as 1 ml syringe.